To be published in "Ground-Based Astronomy in Russia. 21st Century", proceedings of all-Russian conference, September 21-25, 2020 Nizhny Arkhyz, Special Astrophysical Observatory of RAS. Eds: I.I. Romanyuk, I.A. Yakunin, A.F. Valeev, D.J. Kudryavtsev. 8 pages, 4 figures
We give a short review of the current results of studying of star formation sites observed beyond the main discs of galaxies in different interacting systems: Arp 270, Arp 194, Arp 305, NGC 4656 and NGC 90. The observations were carried out at the 6-meter telescope BTA in SAO RAS with the SCOPRPIO-2 spectrograph. The properties of star forming islands, their mass, dynamics, chemical abundances, their possible fate and the mechanisms inspiring star formation, appear to be different in different systems.
How does the tidal debris of minor galaxy mergers contribute to structures in spiral galaxies or in the intergalactic medium? While major mergers are known to create structures such as tidal dwarf galaxies and star clusters within their tidal debris, less is known about minor mergers (mass ratios between a dwarf galaxy and disk galaxy of less than one-third) and their tidal debris. This work surveys 6 nearby minor mergers using optical broad-band and H-alpha narrow-band imaging to characterize star formation in their tidal debris. Young star clusters with ages less than the dynamical age of th…
While major mergers and their tidal debris are well studied, they are less common than minor mergers (mass ratios < 0.3). The peculiar spiral NGC 2782 is the result of a merger between two disk galaxies with a mass ratio of ~4:1 occurring ~200 Myr ago. This merger produced a molecular and H I-rich, optically bright eastern tail and an H I-rich, optically faint western tail. Non-detection of CO in the western tail by Braine et al. suggested that star formation had not yet begun to occur in that tidal tail. However, deep Hα narrowband images show evidence of recent star formation in the western …
Collisional debris around interacting and post-interacting galaxies often display condensations of gas and young stars that can potentially form gravitationally bound objects: Tidal Dwarf Galaxies (TDGs). We summarise recent results on TDGs, which are originally published in Lelli et al. (2015, A&A). We study a sample of six TDGs around three different interacting systems, using high-resolution HI observations from the Very Large Array. We find that the HI emission associated to TDGs can be described by rotating disc models. These discs, however, would have undergone less than one orbit since …
We have used V- and I- band images from the Hubble Space Telescope (HST) to identify compact stellar clusters within the tidal tails of twelve different interacting galaxies. The seventeen tails within our sample span a physical parameter space of HI/stellar masses, tail pressure and density through their diversity of tail lengths, optical brightnesses, mass ratios, HI column densities, stage on the Toomre sequence, and tail kinematics. Our preliminary findings in this study indicate that star cluster demographics of the tidal tail environment are compatible with the current understanding of s…
The environment-dependent bimodality of the distribution of stellar mass ($M_\ast$) and specific star formation rate (sSFR) of galaxies, and its explanation in terms of the central-satellite dichotomy, form a cornerstone of our current understanding of galaxy evolution in the hierarchical structure formation paradigm. We revisit this framework in the IllustrisTNG simulation in the context of the most extreme local tidal anisotropy $α_{\rm peak}$ experienced by each galaxy over cosmic time, which is an excellent proxy for environmental influence. We show that, while sharing a common monotonic $…
We investigate the evolution of the tidal field experienced by massive star clusters using cosmological simulations of Milky Way-sized galaxies. Clusters in our simulations experience the strongest tidal force in the first few hundred Myr after formation, when the maximum eigenvalue of the tidal tensor reaches several times $10^4$ Gyr$^{-2}$. After about 1 Gyr the tidal field plateaus at a lower value, with the median $λ_{\rm m} \sim 3 \times 10^3$ Gyr$^{-2}$. The fraction of time clusters spend in high tidal strength ($λ_{\rm m} > 3 \times 10^4$ Gyr$^{-2}$) regions also decreases with their a…
The properties of tidally induced arms provide a means to study molecular cloud formation and the subsequent star formation under environmental conditions which in principle are different from quasi stationary spiral arms. We report the properties of a newly discovered molecular gas arm of likely tidal origin at the south of NGC 4039 and the overlap region in the Antennae galaxies, with a resolution of 1"68 x 0"85, using the Atacama Large Millimeter/submillimeter Array science verification CO(2-1) data. The arm extends 3.4 kpc (34") and is characterized by widths of ~ 200 pc (2") and velocity …
We explore the effects of tidal interactions on star formation (SF) by analysing a sample of CALIFA survey galaxies. The sample consists of tidally and non-tidally perturbed galaxies, paired at the closest stellar mass densities for the same galaxy type between subsamples. They are then compared, both on the resolved Star Formation Main Sequence (SFMS) plane and in annular property profiles. Star-forming regions in tidally perturbed galaxies exhibit flatter SFMS slopes compared to star-forming regions in non-tidally perturbed galaxies. Despite that the annular profiles show star-forming region…
Recently a theory about the formation of over-densities of stars along tidal tails of globular clusters has been presented, this theory predicts the position and time of formation of such over-densities and was successfully tested with N-body simulations of globular clusters in a point mass galactic potential. In this work we present a comparison between this theory and our simulations using a dwarf galaxy orbiting two differently shaped dark matter halos to study the effects of a cored and a cuspy halo on the formation and evolution of tidal tails. We find no difference using a cuspy or a cor…
Galactic bars are important drivers of galactic evolution, and yet how they impact the interstellar medium and correspondingly star formation, remains unclear. We present simulation results for two barred galaxies with different formation mechanisms, bars formed in isolation or via a tidal interaction, to consider the spatially and temporally varying trends of star formation. We focus on the early (< 1Gyr) epoch of bar formation so that the interaction is clearly identifiable. The nearby NGC 4303 (isolated) and NGC 3627 (interaction history) are selected as observational analogues to tailor th…
Previous studies have shown that dark matter deficient galaxies (DMDG) such as NGC1052-DF2 (hereafter DF2) can result from tidal stripping. An important question, though, is whether such a stripping scenario can explain DF2's large specific frequency of globular clusters (GCs). After all, tidal stripping and shocking preferentially remove matter from the outskirts. We examine this using idealized, high-resolution simulations of a regular dark matter dominated galaxy that is accreted onto a massive halo. As long as the initial (pre-infall) dark matter halo of the satellite is cored, which is co…
In recent years the Sloan Digital Sky Survey has unraveled a new population of ultra-faint dwarf galaxies (UFDs) in the vicinity of the Milky Way (MW) whose origin remains a puzzle. Using a suite of collisionless N-body simulations, we investigate the formation of UFDs in the context of the tidal stirring model for the formation of dwarf spheroidal galaxies in the Local Group (LG). Our simulations are designed to reproduce the tidal interactions between MW-sized host galaxies and rotationally supported dwarfs embedded in 10^9 M_sun dark matter (DM) halos. We explore a variety of inner density …
Like massive galaxies, dwarf galaxies are expected to undergo major mergers with other dwarfs. However, the end state of these mergers and the role that merging plays in regulating dwarf star formation is uncertain. Using imaging from the Hyper Suprime-Cam Subaru Strategic program, we construct a sample of dwarf-dwarf mergers and examine the star formation and host properties of the merging systems. These galaxies are selected via an automated detection algorithm from a sample of 6875 spectroscopically selected isolated dwarf galaxies at $z<0.12$ and $\log(M_\star/M_\odot)<9.6$ from the Galaxy…
It has been suggested that a trail of diffuse galaxies, including two dark matter deficient galaxies (DMDGs), in the vicinity of NGC1052 formed because of a high-speed collision between two gas-rich dwarf galaxies, one bound to NGC1052 and the other one on an unbound orbit. The collision compresses the gas reservoirs of the colliding galaxies, which in turn triggers a burst of star formation. In contrast, the dark matter and pre-existing stars in the progenitor galaxies pass through it. Since the high pressures in the compressed gas are conducive to the formation of massive globular clusters (…
CROCODILE-SIDM: Tidal Formation of Dark Matter-Deficient Galaxies as a Test Case
The University of Osaka（大阪大学）；The University of Tokyo（东京大学）；University of Nevada, Las Vegas（内华达大学拉斯维加斯分校）；EPFL（洛桑联邦理工学院）；Excellence Cluster ORIGINS（ORIGINS卓越集群）；European Southern Observatory (ESO)（欧洲南方天文台）；Universitäts-Sternwarte, Fakultät für Physik（大学天文台，物理学院）
Ultra Compact Dwarf Galaxies (UCDs) and dwarf galaxy nuclei have many common properties, such as internal velocity dispersions and colour-magnitude trends, suggesting tidally stripped dwarf galaxies as a possible UCD origin. However, UCDs typically have sizes more than twice as large as nuclei at the same luminosity. We use a GPU-enabled version of the particle-mesh code \textsc{superbox} to study the possibility of turning nucleated dwarf galaxies into UCDs by tidally stripping them in a Virgo-like galaxy cluster. We find that motion in spherical potentials, where close passages happen many t…
Tidal encounters are believed to be one of the key drivers of galactic spiral structure in the Universe. Such spirals are expected to produce different morphological and kinematic features compared to density wave and dynamic spiral arms. In this work we present high resolution simulations of a tidal encounter of a small mass companion with a disc galaxy. Included are the effects of gas cooling and heating, star formation and stellar feedback. The structure of the perturbed disc differs greatly from the isolated galaxy, showing clear spiral features that act as sites of new star formation, and…
Gravitational collapse of a massive primordial gas cloud is thought to be a promising path for the formation of supermassive blackholes in the early universe. We study conditions for the so-called direct collapse (DC) blackhole formation in a fully cosmological context. We combine a semianalytic model of early galaxy formation with halo merger trees constructed from dark matter $N$-body simulations. We locate a total of 68 possible DC sites in a volume of $20\;h^{-1}\;\mathrm{Mpc}$ on a side. We then perform hydrodynamics simulations for 42 selected halos to study in detail the evolution of th…
As part of a series of papers aimed at understanding the evolution of the Milky Way's Central Molecular Zone (CMZ), we present hydrodynamical simulations of turbulent molecular clouds orbiting in an accurate model of the gravitational potential extant there. We consider two sets of model clouds differing in the energy content of their velocity fields. In the first, self--virialised set, the turbulent kinetic energies are chosen to be close in magnitude to the clouds' self--gravitational potential energies. Comparison with isolated clouds evolving without an external potential shows that the se…
(Abriged) We present analytic models for the formation and evolution of tidal tails and related structures following impulsive disturbances in galaxy collisions. Since the epicyclic approximation is not valid for large radial excursions, we use orbital equations of the form we call p-ellipses. These have been shown to provide accurate representations of orbits in power-law halo potentials. In the case of a purely tidal disturbance the resulting tidal tails have simple structure. Scalings for their maximum lengths and other characteristics as functions of the tidal amplitude and the exponent of…
Using N-body simulations we study the formation and evolution of tidally induced bars in disky galaxies in clusters. Our progenitor is a massive, late-type galaxy similar to the Milky Way, composed of an exponential disk and an NFW dark matter halo. We place the galaxy on four different orbits in a Virgo-like cluster and evolve it for 10 Gyr. As a reference case we also evolve the same model in isolation. Tidally induced bars form on all orbits soon after the first pericenter passage and survive until the end of the evolution. They appear earlier, are stronger, longer and have lower pattern sp…
Abridged: We present a detailed investigation of the morphological distribution and level of star formation and dust obscuration in the nearby tidally distorted galaxy NGC2442. Spitzer images in the IR at 3.6, 4.5, 5.8, 8.0um, and 24um and GALEX images at 1500Å and 2300Å allow us to resolve the galaxy on scales between 240-600pc. We supplement these with archival data in the B, J, H, and K bands. We use the 8um, 24um and FUV (1500Å) emission to study the star formation rate (SFR). We find that globally, these tracers of star formation give a range of results of ~6-11\msun/yr, with the dust-cor…
Observations and simulations have demonstrated that star formation in galaxies must be actively suppressed to prevent the formation of over-massive galaxies. Galactic outflows driven by stellar feedback or supermassive black hole accretion are often invoked to regulate the amount of cold molecular gas available for future star formation, but may not be the only relevant quenching processes in all galaxies. We present the discovery of vast molecular tidal features extending up to 64 kpc outside of a massive z=0.646 post-starburst galaxy that recently concluded its primary star-forming episode. …
Galaxy evolution is generally affected by tidal interactions. Firstly, in this series, we reported several effects which suggest that tidal interactions contribute to regulating star formation (SF). To confirm that so, we now compare stellar mass assembly histories and SF look-back time annular profiles between CALIFA survey tidally and non-tidally perturbed galaxies. We pair their respective star-forming regions at the closest stellar mass surface densities to reduce the influence of stellar mass. The assembly histories and annular profiles show statistically significant differences so that h…
In a series of papers, we present detailed chemo-dynamical simulations of tidal dwarf galaxies (TDGs). After the first paper, where we focused on the very early evolution, we present in this work simulations on the long-term evolution of TDGs, ranging from their formation to an age of 3 Gyr. Dark-matter free TDGs may constitute a significant component of the dwarf galaxy (DG) population. But it remains to be demonstrated that TDGs can survive their formation phase given stellar feedback processes, the time-variable tidal field of the post-encounter host galaxy and its dark matter halo and ram-…
To search for Tidal Dwarf Galaxies (TDGs) and to study star formation in tidal features, we are conducting a large UV imaging survey of interacting galaxies selected from the Arp (1996) Atlas using the GALEX telescope. As part of that study, we present a GALEX UV and SDSS and SARA optical study of the gas-rich interacting galaxy pair Arp 305 (NGC 4016/7). The GALEX UV data reveal much extended diffuse UV emission and star formation outside the disks. This includes a luminous star forming region between the two galaxies, and a number of such regions in tidal tails. We have identified 45 young s…
The formation of globular clusters remains an open debate. Dwarf starburst galaxies are efficient at forming young massive clusters with similar masses as globular clusters and may hold the key to understanding their formation. We study star cluster formation in a tidal debris - including the vicinity of three tidal dwarf galaxies - in a massive gas dominated collisional ring around NGC~5291. These dwarfs have physical parameters which differ significantly from local starbursting dwarfs. They are gas-rich, highly turbulent, have a gas metallicity already enriched up to half-solar, and are expe…
Only a few molecular clouds in the Solar Neighborhood exhibit the formation of only low-mass stars. Traditionally, these clouds have been assumed to be supported against more vigorous collapse by magnetic fields. The existence of strong magnetic fields in molecular clouds, however, poses serious problems for the formation of stars and of the clouds themselves. In this {\em Letter}, we review the three-dimensional structure and kinematics of Taurus --the archetype of a region forming only low-mass stars-- as well as its orientation within the Milky way. We conclude that the particularly low sta…
We present the results of a Keck/DEIMOS survey of Ultra Compact Dwarfs (UCDs) in the Perseus Cluster core. We confirm cluster membership for 14 UCDs, with radial velocities ~5300 km s$^{-1}$. Two of these confirmed Perseus UCDs have extremely blue colours ($B-R < 0.6$ mag), reside in star forming filaments surrounding NGC 1275, and have likely formed as massive star clusters in the last ~100 Myr. We also measure a central velocity dispersion of a third, UCD13 ($σ_0 = 38 \pm 8$ km s$^{-1}$), the most extended UCD in our sample. We determine it to have radius $R_{e} = 85 \pm 1.1$ pc, a dynamical…
We propose that the Ultra-Diffuse Galaxy (UDG) population represents a set of satellite galaxies born in $\sim10^{10}-10^{11}$ M$_\odot$ halos, similar to field dwarfs, which suffer a dramatic reduction in surface brightness due to tidal stripping and heating. This scenario is observationally motivated by the radial alignment of UDGs in Coma as well as the significant dependence of UDG abundance on cluster mass. As a test of this formation scenario, we apply a semi-analytic model describing the change in stellar mass and half-light radius of dwarf satellites, occupying either cored or cuspy ha…
The tidal tails of post-merger galaxies exhibit ongoing star formation far from their disks. The study of such systems can be useful for our understanding of gas condensation in diverse environments. The ongoing star formation in the tidal tails of post-merger galaxies can be directly studied from ultraviolet (UV) imaging observations. The post merger galaxy NGC7252 ("Atoms-for-Peace" galaxy) is observed with the Astrosat UV imaging telescope (UVIT) in broadband NUV and FUV filters to isolate the star forming regions in the tidal tails and study the spatial variation in star formation rates. B…
The formation and evolution of tidal tails like those observed around some globular clusters and dwarf satellite galaxies is examined with an N-body simulation. In particular, we analyse in detail the evolving tidal features of a one-component satellite that is moving on a highly eccentric orbit in the external field of a host galaxy potential like our own. The results show that every time the satellite approaches apogalacticon, a fresh pair of tidal tails becomes notably prominent, and that eventually, the satellite possesses multiple tidal tails via repeating apocentre passages. Accordingly,…
We investigate a sample of 3 dwarf elliptical galaxies in the Virgo Cluster which have significant reservoirs of HI. We present deep optical imaging (from CFHT and KPNO), HI spectra (Arecibo) and resolved HI imaging (VLA) of this sample. These observations confirm their HI content and optical morphologies, and indicate that the gas is unlikely to be recently accreted. The sample has more in common with dwarf transitionals, although dwarf transitionals are generally lower in stellar mass and gas fraction. VCC 190 has an HI tidal tail from a recent encounter with the massive spiral galaxy NGC 42…
Mergers are fundamental to the standard paradigm of galaxy evolution, and provide a natural formation mechanism for supermassive black hole binaries. The formation process of such a binary can have a direct impact on the rate at which stars are tidally disrupted by one or the other black hole, and the luminous signature of the tidal disruption itself can have distinct imprints of a binary companion. In this chapter we review our current understanding of the influence of black hole binarity on the properties of tidal disruption events. We discuss the rates of tidal disruption by supermassive bl…
We introduce the Galaxy Replacement Technique (GRT) that allows us to model tidal stripping of galaxies with very high-mass (m$_{\rm{star}}=5.4\times10^4$~M$_\odot$/h) and high-spatial resolution (10 pc/h), in a fully cosmological context, using an efficient and fast technique. The technique works by replacing multiple low-resolution DM halos in the base cosmological simulation with high-resolution models, including a DM halo and stellar disk. We apply the method to follow the hierarchical build-up of a cluster since redshift $\sim8$ to now, through the hierarchical accretion of galaxies, indi…
We present results from our Giant Metrewave Radio Telescope (GMRT) HI observations of the Arp 305 system. The system consists of two interacting spiral galaxies NGC 4016 and NGC 4017, a large amount of resultant tidal debris and a prominent tidal dwarf galaxy (TDG) candidate projected within the tidal bridge between the two principal galaxies. Our higher resolution GMRT HI mapping, compared to previous observations, allowed detailed study of smaller scale features. Our HI analysis supports the conclusion in Hancock et al. (2009) that the most recent encounter between the pair occurred $\sim$ 4…
In our current interpretation of the hierarchical structure of the universe it is well established that galaxies collide and merge with each other during their lifetime. If massive black holes (MBHs) reside in galactic centres, we expect them to form binaries in galactic nuclei surrounded by a circumbinary disc. If cooling is efficient enough, the gas in the disc will clump and trigger stellar formation in situ. In this first paper we address the evolution of the binary under the influence of the newly formed stars, which form individually and also clustered. We use SPH techniques to evolve th…
Exploring the formation mechanisms of tidal structures in globular clusters of extragalactic origin
Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学前沿天文与天体物理研究所）；School of Physics and Astronomy, Beijing Normal University（北京师范大学物理与天文学院）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；School of Astronomy and Space Science, University of Chinese Academy of Sciences（中国科学院大学天文与空间科学学院）
Tidal disruption events (TDEs) are valuable probes of the demographics of supermassive black holes as well as the dynamics and population of stars in the centers of galaxies. In this Letter, we focus on studying how the debris disk formation and circularization processes can impact the possibility of observing prompt flares in TDEs. First, we investigate how the efficiency of disk formation is determined by the key parameters, namely, the black hole mass $M_{BH}$, the stellar mass $m_\star$, and the orbital penetration parameter $β$ that quantifies how close the disrupted star would orbit arou…
The optical spectroscopic and radio interferometric HI 21 cm-line observations of the blue compact dwarf galaxy Mrk 22 are presented. The Wolf-Rayet (WR) emission line features corresponding to high ionization lines of HeII $λ$4686 and CIV $λ$5808 from young massive stars are detected. The ages of two prominent star forming regions in the galaxy are estimated as $\sim$10 Myr and $\sim$ 4 Myr. The galaxy has non-thermal radio deficiency, which also indicates a young star-burst and lack of supernovae events from the current star formation activities, consistent with the detection of WR emission …
We use the hydrodynamical EAGLE simulation to test if ultra-compact dwarf galaxies (UCDs) can form by tidal stripping by predicting the ages and metallicities of tidally stripped galaxy nuclei in massive galaxy clusters, and compare these results to compiled observations of age and metallicities of observed UCDs. We further calculate the colours of our sample of simulated stripped nuclei using SSP models and compare these colours to observations of UCDs in the Virgo cluster. We find that the ages of observed UCDs are consistent with simulated stripped nuclei, with both groups of objects having…
Recent observations of tidal debris around galaxies have revealed that the structural properties of the spheroidal components of tidally disturbed galaxies are similar to those found in non-interacting early-type galaxies(ETGs), likely due to minor merging events that do not strongly affect the bulge region or to major mergers that happened a long time ago. We show that independently of merger events, tidal features like shells or rings can also arise if the the dark matter is an ultra light scalar field of mass ~10$^{-22}$eV/c$^2$. In the scalar field dark matter (SFDM) model the small mass p…
The lenticular galaxy NGC474 hosts a rich system of tidal shells and streams, some of which are exceptionally bright. Two teams recently presented spectroscopic observations of the brightest shells. These were the first shell spectra ever observed in integrated starlight. The authors studied the stellar populations of the shell, of the center of the galaxy and of its globular clusters. The precise formation scenario for the tidal features of this prominent galaxy however still remained unclear. Here, we add further clues on their formation from the radii of the shells, and we present a scenari…
We have followed up two ultra-diffuse galaxies (UDGs), detected adjacent to stellar streams, with Hubble Space Telescope (HST) imaging and HI mapping with the Jansky Very Large Array (VLA) in order to investigate the possibility that they might have a tidal origin. With the HST F814W and F555W images we measure the globular cluster (GC) counts for NGC 2708-Dw1 and NGC 5631-Dw1 as $2^{+1}_{-1}$ and $5^{+1}_{-2}$, respectively. NGC 2708-Dw1 is undetected in HI down to a 3$σ$ limit of $\log (M_\mathrm{HI}/\mathrm{M_\odot}) = 7.3$, and there is no apparent HI associated with the nearby stellar str…
The formation and evolution of gravitationally bound, star forming substructures in tidal tails of interacting galaxies, called tidal dwarf galaxies (TDG), has been studied, until now, only in idealised simulations of individual pairs of interacting galaxies for pre-determined orbits, mass ratios, and gas fractions. Here, we present the first identification of TDG candidates in fully cosmological simulations, specifically the high-resolution simulations of the EAGLE suite. The finite resolution of the simulation limits their ability to predict the exact formation rate and survival timescale of…
We investigated the evolution of a massive galactic nucleus hosting a super-massive black hole (SMBH) with mass $M_\mathrm{SMBH}=10^8 \mathrm{M}_\odot$ surrounded by a population of 42 heavy star clusters (GCs). Using direct $N$-body modelling, we show here that the assembly of an NSC through GCs orbital decay and merger is efficiently inhibited by the tidal forces exerted from the SMBH. The GCs mass loss induced by tidal forces causes a significant modification of their mass function, leading to a population of low-mass ($<10^4$) clusters. Nonetheless, the GCs debris accumulated around the SM…
Star formation does not occur until the onset of gravitational collapse inside giant molecular clouds. However, the conditions that initiate cloud collapse and regulate the star formation process remain poorly understood. Local processes such as turbulence and magnetic fields can act to promote or prevent collapse. On larger scales, the galactic potential can also influence cloud stability and is traditionally assessed by the tidal and shear effects. In this paper, we examine the stability of giant molecular clouds (GMCs) in the Large Magellanic Cloud (LMC) against shear and the galactic tide …
The galactic tidal interaction is a possible mechanism to trigger the active star formation in galaxies. Recent analyses using the Hi data in the Large Magellanic Cloud (LMC) proposed that the tidally driven colliding HI flows, induced by the galactic interaction with the Small Magellanic Cloud (SMC), triggered high-mass star formation in the southeastern HI Ridge, including R136 and $\sim$400 O/WR stars, and the galactic center region hosting the N44 region. This study performed a comprehensive HI data analysis across the LMC and found that two Hi velocity components defined in the early stud…
NGC147, NGC185 and CassiopeiaII (CassII) have similar positions in the sky, distances and measured line of sight velocities. This proximity in phase space suggests that these three satellites of M31 form a subgroup within the Local Group. Nevertheless, the differences in their star formation history and interstellar medium, and the recent discovery of a stellar stream in NGC~147, combined with the lack of tidal features in the other two satellites, are all indications of complex and diverse interactions between M31 and these three satellites. We use a genetic algorithm to explore the different…
Galaxy mergers are known to host abundant young massive cluster (YMC) populations, whose formation mechanism is still not well-understood. Here, we present a high-resolution galaxy merger simulation with explicit star formation and stellar feedback prescriptions to investigate how mergers affect the properties of the interstellar medium and YMCs. Compared with a controlled simulation of an isolated galaxy, the mass fraction of dense and high-pressure gas is much higher in mergers. Consequently, the mass function of both molecular clouds and YMCs becomes shallower and extends to higher masses. …
